Transformations in Transition-Metal Carbonyls Containing Arsenic: Exploring the Chemistry of [Et4N]2[HAs{Fe(CO)4}3] in the Search for Single-Source Precursors for Advanced Metal Pnictide Materials

The chemistry of [Et4N]2[HAs­{Fe­(CO)4}3] ([Et4N]2[I]) has been explored with the goal of preparing heterometallic compounds for use as single-source precursors to metal pnictide phases. Reaction of AgPF6 with [Et4N]2[I] in THF produces [Et4N]­[HAs­{Fe2(CO)6(μ-CO)­(μ-H)}­{Fe­(CO)4}] in 12% yield, but the yield is improved to 71% if the reaction is carried out with added [Et4N]­[HFe­(CO)4]. The structure possesses rare As–H and {Fe2(CO)6(μ-CO)­(μ-H)} fragments. The addition of [CPh3]­[BF4] to [Et4N]2[I] in THF gives [Et4N]­[Fe3(CO)9(μ-CO)­{μ3-AsFe­(CO)4}] in 45% yield. This compound is also obtained as a minor product from oxidation of [Et4N]2[I] with 1 equiv of AgPF6, AsCl3, SbCl3, or BiCl3 in THF. The cluster consists of an Fe3As tetrahedron with an isolated Fe­(CO)4 unit bound to the arsenic in a spiked-tetrahedral arrangement. Refluxing [Et4N]2[I] with 1 equiv of AgPF6 in THF produces [Et4N]­[(μ-H)2Fe3(CO)9)­{μ3-AsFe­(CO)4}]. This cluster is similar to [Et4N]­[Fe3(CO)9(μ-CO)­{μ3-AsFe­(CO)4}] with the bridging CO being replaced by two bridging hydride ligands. Treatment of [Et4N]2[I] with 1 equiv of Mn­(CO)5Br in THF gives the spirocyclic compound [Et4N]­[{FeMn­(CO)8}­(μ4-As)­{Fe2(CO)6(μ-CO)­(μ-H)}] in 52% yield. Refluxing this cluster in the presence of triethylamine and an additional 1.8 equiv of Mn­(CO)5Br gives [Et4N]­[Fe3(CO)9(μ-CO)­{μ3-AsMn­(CO)4Br-cis}] in low yield. Alternatively, treating [Et4N]­[{FeMn­(CO)8}­(μ4-As)­{Fe2(CO)6(μ-CO)­(μ-H)}] with triflic acid or an oxidant ([Ox] = Cu+, Ag+, Cu2+, CPh3+) in dichloromethane produces the two neutral compounds (μ-H)2Fe3(CO)9{μ3-AsMn­(CO)5} and {FeMn­(CO)8}­(μ4-As)­{Fe2(CO)8} in trace amounts and high yield, respectively. The former could be removed by treatment with base in nonpolar solvents. Neutral {FeMn­(CO)8}­(μ4-As)­{Fe2(CO)8} can then be isolated by filtration and evaporation in 74% yield. An improved synthesis of the known [Fe3(CO)9(μ-CO)­{μ3-PFe­(CO)4}]− as its tetraethylammonium salt is also included. All compounds were characterized by spectroscopy, by ESI-mass spectrometry, and by single-crystal X-ray diffraction.